arm64: kaslr: Set TCR_EL1.NFD1 when CONFIG_RANDOMIZE_BASE=y

TCR_EL1.NFD1 was allocated by SVE and ensures that fault-surpressing SVE
memory accesses (e.g. speculative accesses from a first-fault gather load)
which translate via TTBR1_EL1 result in a translation fault if they
miss in the TLB when executed from EL0. This mitigates some timing attacks
against KASLR, where the kernel address space could otherwise be probed
efficiently using the FFR in conjunction with suppressed faults on SVE
loads.

Cc: Dave Martin <Dave.Martin@arm.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/mm/proc.S

@@ -36,6 +36,12 @@
 #define TCR_TG_FLAGS	TCR_TG0_4K | TCR_TG1_4K
 #endif
 
+#ifdef CONFIG_RANDOMIZE_BASE
+#define TCR_KASLR_FLAGS	TCR_NFD1
+#else
+#define TCR_KASLR_FLAGS	0
+#endif
+
 #define TCR_SMP_FLAGS	TCR_SHARED
 
 /* PTWs cacheable, inner/outer WBWA */
@@ -432,7 +438,8 @@ ENTRY(__cpu_setup)
 	 * both user and kernel.
 	 */
 	ldr	x10, =TCR_TxSZ(VA_BITS) | TCR_CACHE_FLAGS | TCR_SMP_FLAGS | \
-			TCR_TG_FLAGS | TCR_ASID16 | TCR_TBI0 | TCR_A1
+			TCR_TG_FLAGS | TCR_KASLR_FLAGS | TCR_ASID16 | \
+			TCR_TBI0 | TCR_A1
 	tcr_set_idmap_t0sz	x10, x9
 
 	/*